1. Field of the Invention
This invention relates to methods and means for applying surface-mounted solid-state electronic components to printed circuit boards during the board assembly process. More particularly it is concerned with methods and means employing a fixed array of component-dispensing magazines for populating an entire board in a single operation.
2. Prior Art
Since the advent of the semiconductor, the ongoing competetive drive in the electronics industry has been to decrease the size, increase the functional capability and performance, and reduce the cost of solid-state devices and integrated circuits incorporating them.
As a result, advances in the field of component technology now provide virtually unlimited flexibility in integrated circuit design. Similarly, improvements in component packaging, and particularly in the packaging of both passive and active devices for surface-mounting, allow existing circuits to be made more compact and more powerful circuits to be compressed into a given space on the printed circuit board.
Conventionally, during the assembly of a surface-mounted printed circuit board, the components are applied to, and temporarily held in place by a layer of solder paste previously silk-screened on to the metallized mounting pads on the surface of the board. When that surface has been populated, the adhesive is cured to ensure the components will not be released on heating, and the board is heated to reflow the solder. When cooled, the solder connects the components to the electrical circuit and permanently secures them to the board.
To take advantage of the previously mentioned developments, methods and means must be provided for populating the printed circuit board with the resistors, capacitors, inductors, diodes, transistors, small outline integrated circuits ("SOICs"), plastic leaded chip carriers (PLCCs), leadless ceramic chip carriers ("LCCCs"), and other components that make the circuit work. For most applications, hand-assembly is not practical. Automated assembling means are clearly called for.
A great deal of effort has gone into the design and construction of such machines. A number of different approaches have been taken. One of these employs an in-line conveyor, or a numerically controlled cartesian drive system to positioned the board being assembled under a succession of component-dispensing heads which mount each component to the board in its predetermined location. Machines of this type are particularly suitable for high-throughput in a high-volume production line environment, but they are generally limited in the number and variety of components they can handle at one time and relatively difficult to modify for changes in board design.
In another type of assembler, computer-operated robotic devices or relatively fixed dispensing heads select the components from a feeder or feeding station and place them in their intended locations on the board. In the robotic machines the pickup moves in X and Y directions and may rotate as well. In the fixed-head autoassemblers, a removeable table positions the board under the dispenser. These highly sophisticated "pick-and-place" devices are adaptable to dispense practically any surface-mounted component rapidly and with great accuracy. Many of them are provided with computerized vision or other position-sensing means to enhance the accuracy of component placement. Intended primarily for high-precision work, these machines are generally limited to medium or low throughput situations. They are extremely sensitive and require highly skilled personnel for their set up, maintenance and operation. Particularly they are very expensive.
A third type of placement machine incorporates a cartesian table and multiple dispensing heads arranged in succession. The heads are generally mounted on a rotating turret, which allows their jaws, fingers, or suction tubes to pick up a component at a feeding station and place it on the board. These pick-and-place machines are roughly comparable in capability to the previously mentioned robotic and fixed-head assemblers and suffer from the same limitations and deficiencies. These machines are generally somewhat less flexible than the robotic or fixed-head assemblers, and like them, most often have only low- or medium-throughput compacity.
Another class of autoassembler provides for the population of an entire board, or part of a board, in a single operation. Some assemblers of this type utilize a fixed array of pipettes or component-grasping means to place a number of electronic parts in their respective locations at one time. Others transfer the components by means of a template on which each component occupies the position assigned to it on a printed circuit board. Another assembler in this category is exemplified by U.S. Pat. Nos. 4,127,432, 4,375,126, and 4,462,737. These devices apply the electronic modules directly to the surface of the board by means of an array of component-dispensing magazines. This is the approach taken in the present invention, with several novel improvements.
As seen in the previously mentioned patents, conventionally the component-dispensing magazines are vertically supported in a rigid lattice-shaped matrix. The components are positioned in the respective magazines and ejected from the magazines by means of one or more sets of rods or pistons which are thrust axially into the magazines. These devices suffer from several serious limitations. For one, the physical constraints imposed by the structure of the matrix itself limits the user's ability to positioned the electronic components on the surface of the printed circuit board. In practice, this limitation mandates that the circuit be designed to conform to the geometry of the lattice work. This requirement is unacceptable for all but the most rudimentary circuit designs.
Similarly, the structure of the matrix narrowly limits the size, shape and polar orientation of the components it is capable of assembling.
Additionally, the mass of the lattice structure limits the density with which the components can be assembled on the board's surface. To reduce the mass of the lattice by employing thinner structural members will result in a weakening of the structure supporting the magazines and the integrity of the assembly apparatus.
Still further, these prior art devices must provide a push-rod assembly for each of the through-holes in the matrix which could be occupied by a magazine, even though in operation the majority of those positions would not in fact be occupied. The use of push-rods driven by a common drive mechanism necessitates the provision of means for compensating for differences in thickness of the various components. These thickness-compensating means, likewise, must be provided for at each of the through-hole positions, whether components are to be dispensed at those positions or not. The complexity of these mechanisms makes them costly to manufacture and difficult to maintain, and severely limits the ability of these machines to respond to changes in circuit design. A principle object of the present invention is to provide a method and means for applying surface-mounted electronic components to printed circuit boards, which offers all of the advantages, and avoids the defficiencies inherent in devices of the type described.
More particularly, an object of this invention is the provision of a novel fixture for positioning a plurality of surface-mounted electronic component dispensing magazines for use in a circuit board assembling apparatus.
Another object is the provision of a surface-mounting assembling machine incorporating the aforementioned fixture.
Still another object is the provision of a fixture and assembly machine of the aforementioned type, which are capable of positioning a large number of surface-mounted components in an single operational step with great accuracy and assured repeatability.
A further object is the provision of a surface-mounting apparatus of the type mentioned, having a minimum number of moving parts requiring machine-disabling maintenance.
A further object is the provision of an assembly machine which can be modified rapidly and easily to conform to changes in printed circuit design, and which does not require highly-skilled personnel for set up, operation or modification.
A still further object is the provision of an apparatus of the type mentioned, which has the capacity to dispense electronic components of widely varying size and configuration, in any orientation, at any selected position in any desired printed circuit design.